1. Field of the Invention
The present invention relates to a printing apparatus, a printing method for printing an image on a printing medium using color inks of a plurality of colors containing pigments and a colorless ink, and a data generating apparatus.
2. Description of the Related Art
Demand has recently arisen for an inkjet printing apparatus capable of forming an image with high color reproducibility on a glossy printing medium whose surface is glossy. To meet this demand, there is known an inkjet apparatus which adopts a red spot color ink in addition to basic, cyan, magenta, yellow, and black color inks to, for example, widen the color reproductive range.
The need is also high for an inkjet printing apparatus using a pigment ink higher in image fastness than a dye ink. However, most pigment inks hardly permeate into a printing medium. Especially in image formation on a glossy printing medium, the heterogeneity of glossiness readily occurs between the printed and unprinted portions of an image.
To solve this problem of the pigment ink, there is proposed a technique of adjusting the gloss of a printed portion by setting the discharge amount of image quality improvement liquid (colorless ink) based on the color ink amount (see, for example, Japanese Patent No. 3591534). This technique reduces the heterogeneity of glossiness by applying a colorless ink intensively to a region having a small color ink amount when forming an image on a highly glossy printing medium.
However, the present inventors have made studies and found that the technique disclosed in Japanese Patent No. 3591534 has the following problem. That is, when the gloss or surface smoothness of a printed portion changes upon printing with a colorless ink, even the tint seems different. Especially at a dark image portion, applying a colorless ink impairs the surface smoothness and hinders implementation of a wide color reproductive range. When, therefore, forming an image on a glossy printing medium using a pigment ink, the color reproductive range cannot be satisfactorily adjusted by only setting the colorless ink discharge amount based on the color ink amount. The conventional technique cannot fully meet the user demand for an image having a wide color reproductive range over an image having high gloss uniformity.